WASHINGTON — Officials are investigating after a prominent part of Washington’s skyline went dark.

The National Park Service tweeted Tuesday night that the Washington Monument’s lights went out around 7 p.m. Officials later said they believe there’s a problem with the automated program that controls the monument’s lights and electricians will be able to confirm whether that is the problem on Wednesday morning.

The monument has been closed to visitors since August because of ongoing problems with its elevator, which carries visitors to an observation deck near the top of the 555-foot-tall monument. It usually draws 600,000 visitors a year.

In December, officials announced a $2 million to $3 million project to modernize the elevator. The monument is expected to reopen to visitors in 2019.